Skin conditions include some of the most common disorders treated in the developing world and represent a significant economic burden, incurring an estimated cost of about $39.3 billion in 2004 in the U.S. alone. (“The Burden of Skin Disease 2004,” Prepared for The Society for Investigative Dermatology and The American Academy of Dermatology Association by The Lewin Group, Inc. 2006.) At any moment, one-third of the U.S. population is estimated to actively suffer from at least one skin condition. (Johnson, “Skin conditions and related need for medical care amount persons 1-74 years, United States, 1971-1974.” Vital and Health Statistics, Series 11, No. 212, DHEW publication No. (PHS) 79-1660, U.S. Department of Health, Education and Welfare, National Center for Health Statistics 1978: 1-72.) Different skin conditions are associated with widely varied triggers, biological mechanisms, environmental factors, and clinical manifestations, complicating research into skin homeostasis and development of skin care agents with broad applicability.
Acne is a disorder characterized by skin eruptions (including comedones, papules, pustules, and cysts), which commonly occur in areas having a high density of sebaceous glands, including the face, neck, chest, back and shoulders. The skin eruptions occur, for example, when hair follicles are blocked with sebum and dead skin cells. The lesions may be accompanied by inflammation; bacteria, such as Propionibacterium acnes, thrive within clogged pores and trigger an inflammatory response. Several factors are believed to contribute to the onset and severity of acne. Although the physical changes within the skin that lead to acne eruptions have been characterized, the underlying causes that dictate which follicles will be affected have proven difficult to identify. Hormonal changes caused by stress, puberty, medications, and pregnancy can increase acne break-outs. Genetic factors also influence the prevalence of acne. Environmental factors, including heat, humidity, and the use of oily or occlusive skin products can also result in acne flare-ups. Diets high in carbohydrates can lead to a worsening of acne (see Smith et al., J Amer Acad of Dermatol, 57 (2): 247-56 (2007)). The development of acne treatments has been hindered because, in part, the root cause of the disorder is not well understood and a myriad of factors may (or may not) play a role in the skin condition. Most current therapies are aimed at treating acne after skin eruptions have occurred to prevent recurring break-outs.
Eczema, also known as dermatitis, is a large class of skin disorders characterized by inflammation leading to red and itchy skin, blisters, and fissures. Eczema is estimated to affect approximately 1 in 10 people world-wide. Types of eczema include neurodermatitis, contact, seborrheic, nummular, and dyshidrotic eczema. The exact cause of eczema is unknown, although the disorder is believed to be influenced by genetic factors, such as a predisposition to allergies or other hypersensitivity. Eczema also has been linked with environmental factors including dry air, cold, and skin irritants. Stress and illness are believed to exacerbate the condition.
Atopic dermatitis, considered a form of eczema, is a chronic skin disorder characterized by scaly and itchy rashes. The disorder can also manifest as skin lesions, discoloration, and eye disorders. Several causes of the disorder have been proposed; however, none have been identified with certainty. Environmental allergens, including food, dust, pollen, and dander, have been linked to the disease. Genetic factors are considered to play a role in the onset of the disease based on family studies (Kluken et al., Allergy, 58(1):5-12 (2003)). Atopic dermatitis has also been linked to changes in genes that lead to defects in the epidermal barrier (Cork et al., J Invest Dermatol., 129(8):1892-908 (2009)). Environmental factors also influence the development of the disorder; atopic dermatitis has been associated with exposure to radiation from microwaves and cell phones (see, e.g., Kimata et al., Int Arch of Allergy and Immunology, 129 (4):348-350 (2002), and Wang et al., Pediatr Allergy Immunol., 18(5):441-7 (2007)).
Dandruff, alternatively referred to in the literature as ptyriasis simplex, furfuracea or capitis, is a skin disorder characterized by flaking, itching and microinflammation. Dandruff is considered to be a form of seborrheic dermatitis, which may be found in other locations on the body. Generally, dandruff is considered the mildest form of seborrheic dermatitis from a clinical perspective since inflammation is minimal and typically subclinical. In fact, as recently as a decade ago the dandruff condition was thought to be non-inflammatory. Seborrheic dermatitis generally is associated with a higher degree of inflammation.
The pathogenesis of dandruff is complex, and appears to be the result of interactions between scalp skin, cutaneous microflora and the cutaneous immune system. The key clinical features of dandruff include flaking and itch, and the precise underlying events that provoke these symptoms are incompletely understood. Dandruff is considered to have multiple, sometimes overlapping, causes with numerous pathogenic pathways and complex mechanisms. A microbial flora, including, for example, Malassezia spp, is implicated in the most common forms of dandruff. Yet, no relationship has been found between severity of symptoms and fungal count. Scaling conditions similar to dandruff may occur following excessive exposure to sunlight, minor chronic irritation of the scalp, over-brushing, over-shampooing, certain cosmetic hair products, and irritation from airborne substances, and psychological stress.
Psoriasis is a chronic disease characterized by an excessive build-up of skin cells. The clinical manifestations of disorder are diverse, and often include plaques of silvery skin, itching, swelling, lesions, and pustules. The flares can occur randomly on different parts of the body. The disease is generally classified into five subtypes, plaque, guttate, inverse, pustular and erythrodermic, each of which are associated with unique characteristics. Severe cases of psoriasis can result in disfigurement and disability. For example, pustular psoriasis can lead to systemic symptoms including fever, chills, weight loss, nausea, headache, joint pain, and fatigue.
The cause of psoriasis and its characteristic overgrowth of skin cells is not well-understood. One hypothesis proposes that the disease is mediated by defects in the immune system, and the disease is believed to have a strong genetic component. Chromosomal loci associated with susceptibility to psoriasis have been identified. Environmental triggers, including injury, smoking, medication, and cold weather, are believed to exacerbate the condition and potentially trigger recurrences. Current treatments seek to minimize the severity of existing flare-ups and minimize recurrence. Many existing treatments, including Enbrel®, Remicade®, and Humira® target the immune system.
Despite the prevalence of skin conditions and research efforts to identify their causes, the underlying mechanisms responsible for many skin conditions remain unclear. The pathogenesis of each, individual condition is multifactorial, and the complex etiologies associated with skin conditions are influenced by a combination of genetic and environmental factors unique to each condition. Indeed, the diverse external and internal stimuli associated with different skin conditions, in combination with an individual's predisposition, and etiological complexity makes a broad spectrum treatment a challenge. There is a persistent need in the art for material and methods for studying the underlying biology of multiple skin conditions, identifying potential skin active agents without reliance on mechanism of action or etiology of a particular condition(s), and determining the influence of agents on skin homeostasis.
The present investigators undertook a transcriptomics investigation of seemingly diverse skin conditions and explored the application of “connectivity mapping” (C-map) to the search for new skin-active agents with broad spectrum efficacy. The general notion that functionality could be accurately determined for previously uncharacterized genes, and that potential targets of drug agents could be identified by mapping connections in a data base of gene expression profiles for drug-treated cells, was spearheaded in 2000 with publication of a seminal paper by T. R. Hughes et al. [“Functional discovery via a compendium of expression profiles” Cell 102, 109-126 (2000)], followed shortly thereafter with the launch of The Connectivity Map (-map Project by Justin Lamb and researchers at MIT (“Connectivity Map: Gene Expression Signatures to Connect Small Molecules, Genes, and Disease,” Science, Vol 313, 2006.) In 2006, Lamb's group began publishing a detailed synopsis of the mechanics of C-map construction and installments of the reference collection of gene expression profiles used to create the first generation C-map and the initiation of an on-going large scale community C-map project, which is available under the “supporting materials” hyperlink at the sciencemag.org website.
Connectivity mapping has achieved in confirmed medical successes with identification of new agents for the treatment of various diseases, including cancer. Nonetheless, certain limiting presumptions challenge application of C-map with respect to diseases of polygenic origin or conditions that are characterized by diverse, and often apparently unrelated, cellular phenotypic manifestations (such as skin conditions). According to Lamb, the challenge to constructing a useful C-map is in the selection of input reference data which permit generation of clinically salient and useful output upon query. For the drug-related C-map of Lamb, strong associations comprise the reference associations, and strong associations are the desired output identified as “hits.”
However, agents suitable as pharmaceutical agents and agents suitable as cosmetic agents are categorically distinct. Pharmaceutical agents are selected for specificity and are intended to have measurable effects on structure and function of the body, while cosmetic agents are selected for effect on appearance and may not affect structure and function of the body to a measurable degree. Cosmetic agents also tend to be non-specific with respect to effect on cellular phenotype, and administration to the body is generally limited to application on or close to the body surface.
In constructing C-maps relating to pharmaceutical agents, Lamb stresses that particular difficulty is encountered if reference connections are extremely sensitive and at the same time difficult to detect (weak), and Lamb adopted compromises aimed at minimizing numerous, diffuse associations. Since the regulatory scheme for drug products requires high degrees of specificity between a purported drug agent and disease state, and modulation of disease by impacting a single protein with a minimum of tangential associations is desired in development of pharmaceutical actives, the Lamb C-map is well-suited for screening for potential pharmaceutical agents despite the noted compromises.
The connectivity mapping protocols of Lamb would not be predicted, therefore, to have utility for hypothesis testing/generating in the field of cosmetics and skin care, particularly given the compromises described above. Skin care formulators seek agents or compositions of agents capable of modulating multiple targets and having effects across complex phenotypes and conditions. Further, the phenotypic impact of a skin care agent must be relatively low by definition, so that the agent avoids being subject to the regulatory scheme for pharmaceutical actives. Nonetheless, the impact must be perceptible to the consumer and preferably empirically confirmable by scientific methods. Gene transcription/expression profiles for cosmetic conditions are generally diffuse, comprising many genes with low to moderate fold differentials. Cosmetic agents, therefore, provide more diverse and less acute effects on cellular phenotype and generate the sort of associations expressly taught by Lamb as unsuitable for generating connectivity maps useful for confident hypothesis testing.
Nonetheless, contrary to the teachings of Lamb and the prior art in general, the present investigators surprisingly discovered that useful connectivity maps could be developed to evaluate skin-care actives and cosmetic agents, despite the highly diffuse, systemic and low-level effects these sorts of actives generally engender. Additionally, the value of a connectivity map approach to discover functional connections shared by unhealthy skin phenotypes and study the effects of agents on skin homeostasis is counter-indicated by the progenitors of the drug-based C-map; the relevant phenotypes are very complex, skin condition etiology is not well understood, the genetic perturbations are numerous and weak, and cosmetic agent action is likewise diffuse and, by definition, relatively weak. The successful application of connectivity mapping to target a plurality of biological conditions, each of which is multi-factored and poorly delineated, is a breakthrough in skin care research.